One reason is perspective. Another is life experiences. Another is general alertness and powers of observation. There are more.
Take perspective. In witnessing an accident and then telling the police what was seen, a lot of it depends on how far the actual incident was from the person recounting it. Were they in the car immediately behind or next to the involved car when it happened? Were they in a shop along the street where it happened or walking along on the sidewalk?
Were they actually looking in that direction and focused on what happened. Obviously, they weren't told to be ready to notice what was about to happen so they could pay close attention to it. If they were several feet away, was there anything between them and what happened that blocked some or most of their view - or distracted them or captured their attention?
Sometimes people use their life experiences to mentally recall what could have happened or what they think happened in a case like this and believe that they really saw it happen that way when, in fact, they didn't. Sometimes it will seem as though it must have happened a certain way so we will tend to believe that or add that to our recollection. We didn't actually get a clear view of what happened, but we think we know anyway.
If we were distracted or focusing on something else at the time and then drawn into what happened by the sound of it, we weren't really prepared to observe it. However, our minds may tell us what we think must have happened or what it appears to be and we'll go with that version. We might even recall to the police that we saw it happen even though we didn't focus on the actual even until a split second or so after it happened.
So, with all of these challenges in watching something happen, or being close enough that we think we saw what happened, it's not surprising that there are so many varied accounts of the same event. Now, apply this experience to making an assessment of someone's home.
When we look at a potential client's kitchen, bathroom, or other area that is presenting issues or challenges for them, are we looking at it totally objectively, or are we filtering it based on our own life experiences? Are we projecting our own lifestyle and living habits onto our clients in making a determination of what is going on and what might need to be changed? Are we hearing our clients describe what they want or what they are doing currently and allowing that to affect how we evaluate the space?
These certainly are challenges in how we approach our work. We're all human, and we want to empathize with our clients. remaining totally objective often is quite the task.